Analysis of circulating lipid-phase micronutrients in humans by HPLC: review and overview of new developments

Retinol, tocopherols, coenzyme Q10, carotenoids, and vitamin D are lipophilic compounds shown to function as important health-protective agents by mitigating the damaging effects of oxidative and other injury. Scientific interest in evaluating these compounds has resurfaced in recent years, particularly in the nutritional, clinical and epidemiologic fields, and has precipitated the development of a multitude of new analytical techniques. This review considers recent developments in HPLC-based assays since 2007 for the simultaneous determination of these lipid-phase compounds utilizing exclusively serum or plasma as these matrices are mostly used in clinical and epidemiological investigations. We also provide an overview of blood measurements for selected carotenoids, tocopherols, coenzyme Q10 and retinol from the last 15years of healthy umbilical cord blood, children, and adults.

Selenium losses in 10 burned patients

To determine the selenium (Se) losses and balances, 10 patients with burns of 32 +/- 9% (mean +/- SD) of total body surface and aged 36 +/- 9 years were studied from D1 (first post-injury) unitl D7. Cutaneous losses were extracted from the textiles surrounding the patients. Serum and urine were collected until D20. Exudative losses of nitrogen decreased progressively (mean 8.7 +/- 3.8 g/24H). Se was detectable in wound seepage only during excision-grafting: mean operative loss was 342 +/- 191 mug. Mean urinary Se excretion was 41 +/- 13 mug/24H. Operative cutaneous losses led to some negative balances. Serum Se and glutathione peroxydase (GSHPx) were depressed until D20. Serum Se was related to N intake (p < 0.001). The decreased Se and GSHPx levels reflect a deficiency state, which measured losses did not explain, but limitations of the measurement methods prevented detection of Se cutaneous losses 100 mug/24H.

Alpha-Tocopherol Distribution in Lipoproteins and Anti-Inflammatory Effects Differ between CHD-Patients and Healthy Subjects

OBJECTIVE

The purpose of this study was to investigate the dose-dependent effects of RRR-alpha-tocopherol supplementation in coronary heart disease (CHD) patients and healthy subjects on plasma alpha-tocopherol levels, plasma lipoprotein distribution, LDL oxidation, and inflammatory plasma markers.

METHODS

12 patients with coronary heart disease and 12 healthy subjects were supplemented with increasing dosages of RRR-alpha-tocopherol at 100, 200 and 400 mg/day for a period of 3 weeks per dose. Lipoproteins were separated by FPLC and ultracentrifugation. Alpha-tocopherol was measured by HPLC. Resistance of LDL to oxidation was determined by reading the absorption at 234 nm after CuCl2-induced oxidation. Clinical chemistry and inflammatory markers were measured on automated analysis systems.

RESULTS

Plasma alpha-tocopherol concentrations at baseline were comparable between CHD-patients and healthy subjects (21.7 +/- 4.7 micromol/L and 25.8 +/- 7.6 micromol/L, respectively). CHD-patients showed a significant increase (59%) of plasma alpha-tocopherol concentrations to 34.6 +/- 9.8 micromol/L at a dosage of 100 mg/day RRR-alpha-tocopherol, whereas healthy subjects showed a significant (54%) increase to 39.7 +/- 6.1 micromol/L only with 400 mg/day RRR-alpha-tocopherol. In addition, CHD-patients showed a significantly increased enrichment of alpha-tocopherol in VLDL. Supplementation (200 mg/day) caused a significant decrease of the acute phase plasma proteins C-reactive protein (CRP) (-65%) and fibrinogen (-24%).

CONCLUSION

Our data demonstrate that CHD-patients require lower dosages of alpha-tocopherol supplementation than healthy subjects to exert biological effects on plasma lipoproteins and acute phase response.

Nebivolol decreases oxidative stress in essential hypertensive patients and increases nitric oxide by reducing its oxidative inactivation

OBJECTIVE

To obtain further insight into the mechanism underlying the vasodilator effect of nebivolol. Since oxidative inactivation of nitric oxide (NO) is regarded as an important cause of its decreased biological activity, we studied (1) the effect of nebivolol on some oxidative parameters in essential hypertensive patients; (2) the effect of plasma of nebivolol-treated patients on reactive oxygen species production and NO availability in endothelial cells.

METHODS

A total of 20 healthy subjects and 20 matched essential hypertensive patients treated with atenolol or nebivolol according to a double-blind, randomized design participated in the study. We measured low-density lipoprotein (LDL) and plasma hydroperoxides, 8-isoprostanes, oxidized LDL, susceptibility of LDL to oxidation (lag phase) and LDL vitamin E and the effect of plasma of nebivolol- and atenolol-treated patients on reactive oxygen species production and NO availability in endothelial cells exposed to oxidative stress.

RESULTS

In hypertensive patients, nebivolol and atenolol significantly reduced blood pressure values after 4 weeks of treatment. Plasma and LDL hydroperoxides, plasma 8-isoprostanes, plasma ox-LDL and LDL lag phase were significantly improved only in the patients receiving nebivolol compared with the atenolol group. Similarly there was a reduction of reactive oxygen species (ROS) and O2*- concentration in endothelial cells exposed to oxidative stress after incubation of the cells with plasma of the patients enrolled in the trial only in the patients receiving nebivolol compared to atenolol group. Furthermore, the reduction of basal and stimulated NO induced by oxidative stress in endothelial cells was significantly lower in the patients receiving nebivolol compared to atenolol group.

CONCLUSIONS

The findings of the present study indicate that nebivolol, through its antioxidant properties, increases NO also by decreasing its oxidative inactivation.

Vitamin C deficiency exerts paradoxical cardiovascular effects in osteogenic disorder Shionogi (ODS) rats

Vitamin C is considered to be a very efficient water-soluble antioxidant, for which several new cardiovascular properties were recently described. The aim of this study was to determine in vivo the effects of a severe depletion of vitamin C on cardiac and vascular variables and reperfusion arrhythmias. For this purpose, we used a mutant strain of Wistar rats, osteogenic disorder Shionogi (ODS). After 15 d of consuming a vitamin C-deficient diet, ODS rats had a 90% decrease in plasma and tissue levels of ascorbate compared with ODS vitamin C-supplemented rats and normal Wistar rats. However, plasma antioxidant capacity, proteins, alpha-tocopherol, urate, catecholamines, lipids, and nitrate were not influenced by the vitamin C deficiency in ODS rats. Moreover, there was no difference between ODS vitamin C-deficient and -supplemented rats in heart rate and arterial pressure. After 5 min of an in vivo regional myocardial ischemia, various severe arrhythmias were observed, but their intensities were not modified by vitamin C in vitamin C-deficient ODS rats. The vascular reactivity, measured in vitro on thoracic arteries, was not altered by ascorbate deficiency in ODS rats. These unexpected results suggest that unidentified compensatory mechanisms play a role in maintaining normal cardiac function and vascular reactivity in vitamin C-deficient rats.

Protective effect of supplementation of fish oil with high n-3 polyunsaturated fatty acids against oxidative stress-induced DNA damage of rat liver in vivo

The present study was undertaken to know the effect of supplementation of fish oil with high n-3 polyunsaturated fatty acids (PUFA) on oxidative stress-induced DNA damage of rat liver in vivo. Male Wistar rats were fed a diet containing fish oil or safflower oil with high n-6 PUFA at 50 g/kg of diet and an equal amount of vitamin E at 59 mg/kg of diet for 6 weeks. Livers of rats fed fish oil were rich in n-3 PUFA, whereas those of rats fed safflower oil were rich in n-6 PUFA. Ferric nitrilotriacetate was intraperitoneally injected to induce oxidative stress. The degree of lipid peroxidation of the liver was assessed by the levels of phospholipid hydroperoxides and thiobarbituric acid-reactive substances (TBARS), and the degree of oxidative DNA damage was assessed by comet type characterization in alkaline single-cell gel electrophoresis and 8-hydroxy-2'-deoxyguanosine levels. The levels of TBARS of the livers of the fish oil diet group increased to a greater extent than those of the safflower oil diet group, whereas the levels of the hydroperoxides of the livers of both diet groups increased to a similar extent. The vitamin E level of livers of the fish oil diet group was remarkably decreased. The degree of DNA damage of both diet groups was increased, but the increased level of the fish oil diet group was remarkably lower than that of the safflower oil diet group. The above results indicate that fish oil supplementation does not enhance but appears to protect against oxidative stress-induced DNA damage and suggest that lipid peroxidation does not enhance but lowers the DNA damage.

Effect of supplementation of n-3 polyunsaturated fatty acids on oxidative stress-induced DNA damage of rat hepatocytes

The effect of supplementation of n-3 polyunsaturated fatty acids (PUFA) on oxidative stress-induced DNA damage of rat hepatocytes was examined. Male Wistar rats were fed a diet containing safflower oil (control n-6 PUFA diet) or fish oil (n-3 PUFA diet) in 50 g/kg of dried diet and an equal amount of vitamin E in 59 mg/kg of dried diet for 6 weeks. The liver of rats fed safflower oil was rich in n-6 PUFA, whereas that of rats fed fish oil was rich in n-3 PUFA. Isolated hepatocytes were treated in vitro with ADP/Fe (II) ion or hydrogen peroxide at 37 degrees C for 30 min to induce oxidative stress. The degree of lipid peroxidation was assessed by the levels of phospholipid hydroperoxides and thiobarbituric acid-reactive substances. The degree of oxidative DNA damage was assessed based on comet-type characterization in alkaline single-cell gel electrophoresis and 8-hydroxy-deoxyguanosine levels. In both ADP/Fe(II) ion and hydrogen peroxide oxidation, the degree of lipid peroxidation of hepatocytes increased in both diet groups, and the level of increase in the fish oil diet group was slightly higher than that in the safflower oil diet group. In ADP/Fe(II) ion oxidation, the degree of DNA damage increased in both diet groups, but there were no significant differences in the level of increase. In contrast, in hydrogen peroxide oxidation, the degree of DNA damage increased in both diet, and the increase in the fish oil diet group was significantly lower than that in the safflower oil diet group. It is unlikely that an n-3 PUFA-rich diet enhances oxidative stress-induced hepatocyte DNA damage as compared with the control n-6 PUFA-rich diet.

Quantity versus quality of LDL cholesterol in patients with familial hypercholesterolemia--which is more important?

BACKGROUND

The aim of this study was to determine the effects of low-density lipoprotein (LDL) particle size and composition on the susceptibility of LDL to oxidation in subjects with Familial Hypercholesterolemia (FH).

METHODS

LDL was isolated from 20 FH homozygotes, 20 FH heterozygotes and 20 normal controls. Susceptibility of LDL to ex vivo copper-mediated oxidation was assessed by measuring conjugated diene production at 234 nm. Other factors known to influence LDL oxidation, namely particle size, vitamin E levels, and fatty acid composition of the LDL particles were also measured.

RESULTS

The mean duration of the lag phase was 1.42-fold longer in the FH homozygotes, and 1.21-fold longer in the FH heterozygotes than in the normal controls. LDL particle size was significantly larger in the FH homozygotes (26.45+/-0.37 nm) and FH heterozygotes (26.01+/-0.40 nm) compared to the normal control group (25.17+/-0.39 nm). LDL vitamin E concentrations, when expressed relative to LDL cholesterol concentrations, were similar in all the groups. In addition, no significant differences were observed in the total saturated, monounsaturated or polyunsaturated fatty acid content of LDL in the three groups of subjects.

CONCLUSION

These results suggest that it is the great excess in LDL quantity, rather than LDL 'quality', that is responsible for the severe and premature atherosclerosis in patients with FH.

Effects of a high polyunsaturated fat diet and vitamin E supplementation on high-density lipoprotein oxidation in humans

Oxidative modification of high-density lipoproteins (HDL) impairs several biologic functions critical to its role in reverse cholesterol transport. We therefore investigated the effect of dietary polyunsaturated fat and vitamin E on the kinetics of HDL oxidation. Ten subjects were fed sequentially: a baseline diet in which the major fat source was olive oil; a high polyunsaturated fat diet in which the major fat source was safflower oil; and the safflower oil diet plus 800 I.U. vitamin E per day. Plasma lipoprotein levels, vitamin E content, fatty acid composition, and oxidation lag time and rate were determined after 3 weeks on each diet. The polyunsaturated fat diet increased the mean HDL(2) lag time from 45.8+/-12.5 to 83.3+/-11.6 min with no change in oxidation rate. Addition of vitamin E further increased the HDL(2) lag time to 115.6+/-4.4 min and decreased the HDL(2) oxidation rate 10-fold. Neither the polyunsaturated diet alone nor the diet with vitamin E supplementation had any effect on HDL(3) oxidation. We conclude that under conditions of controlled dietary fat intake, a high polyunsaturated fat intake does not increase the oxidation susceptibility of HDL subfractions, and that in this setting, vitamin E supplementation reduces the oxidation susceptibility of HDL(2). These data suggest that antioxidants could influence HDL function in vivo.

Oxidative stress in pre-eclampsia

BACKGROUND

The objective of this study was to test the hypothesis that maternal plasma, cord plasma and placental tissue lipid peroxidation products are increased and antioxidants are decreased in women with pre-eclampsia.

METHODS

Placenta, maternal and cord plasma were collected at delivery from 29 normal, 21 pre-eclamptic and six eclamptic women. Plasma was collected from 21 non-pregnant matched controls. The analyses were measured by HPLC and colorimetric assay.

RESULTS

Plasma maternal concentrations of uric acid, LPO, MDA, ascorbic acid, vitamin E and cholesterol were not significantly different in pre-eclampsia as compared with normal pregnancy. Plasma concentrations of ascorbic acid and vitamin E were not significantly different in normal pregnancy as compared with the non-pregnant controls. Cord plasma concentrations of MDA were significantly higher in eclampsia (1.16+/-0.26 micromol/l) as compared with normal pregnancy (0.79+/-0.05 micromol/l, p<0.02) and pre-eclampsia (0.83+/-0.05 micromol/l, p<0.05). Cord plasma concentrations of vitamin E were significantly higher in eclampsia (21.3+/-7.5 micromol/l) as compared with normal pregnancy (10.2+/-1.1 micromol/l, p<0.01) and pre-eclampsia (10.4+/-1.8 micromol/l, p<0.04). Placental concentrations of LPO, MDA and ascorbic acid were not significantly different in pre-eclampsia as compared with normal pregnancy. Plasma cord concentrations of LPO and placental concentrations of vitamin E were undetected for normal pregnant, pre-eclamptic and eclamptic women respectively. Uric acid concentrations were significantly increased in eclampsia as compared with the non-pregnant controls (p<0.0001), normal pregnant controls (p<0.0001) and pre-eclampsia (p<0.008).

CONCLUSIONS

The findings in this study do not show any evidence of deficiency in the maternal protective antioxidant systems or increased production of lipid peroxidation products, LPO and MDA in African women with pre-eclampsia as compared with normal pregnancy. However, there was evidence of increased cord plasma concentrations of MDA and vitamin E in eclampsia as compared with normal pregnancy and pre-eclampsia. The placenta may be effective in removing MDA. The antioxidant uric acid serves as a protective role whilst the antioxidant and oxidant capacity in the different study groups remained unchanged.

Pro-oxidant effect of vitamin E in cigarette smokers consuming a high polyunsaturated fat diet

Dietary polyunsaturated fats and vitamin E are associated with reduced risk for atherosclerosis, but in smokers, they could promote lipid oxidation. Therefore, we examined the effects of a high polyunsaturated fat diet and vitamin E supplementation on measures of lipid oxidation in cigarette smokers. Ten subjects who smoked >1 pack of cigarettes per day were sequentially fed the following: a baseline diet in which the major fat source was olive oil, a diet in which the major fat source was high-linoleic safflower oil, and finally, the safflower oil diet plus 800 IU vitamin E per day. LDL oxidation lag time and rate and plasma total F(2)-isoprostanes and prostaglandin F(2alpha) (PGF(2alpha)) were determined after 3 weeks on each diet. The safflower oil diet increased total F(2)-isoprostanes from 53.0+/-7.2 to 116.2+/-11.2 nmol/L and PGF(2alpha) from 3.5+/-0.2 to 5.5+/-0.5 nmol/L, without changing LDL oxidation parameters. Addition of vitamin E prolonged mean LDL oxidation lag time but, paradoxically, further increased F(2)-isoprostanes to 188.2+/-10.9 nmol/L and PGF(2alpha) to 7.8+/-0.4 nmol/L. These data suggest that vitamin E may function as a pro-oxidant in cigarette smokers consuming a high polyunsaturated fat diet.

The effect of concentrated n-3 fatty acids versus gemfibrozil on plasma lipoproteins, low density lipoprotein heterogeneity and oxidizability in patients with hypertriglyceridemia

We evaluated in a double-blind randomized trial with a double-dummy design in 28 patients with primary hypertriglyceridemia, the effect of gemfibrozil (1200 mg/day) versus Omacor (4 g/day), a drug containing the n-3 fatty acids eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), on lipid and lipoprotein levels, low density lipoprotein (LDL) subfraction profile and LDL oxidizability. Both Omacor and gemfibrozil therapy resulted in a similar significant decrease in serum triglyceride (TG), very low density lipoprotein (VLDL) triglyceride and VLDL cholesterol concentrations and an increase in high density lipoprotein (HDL) and LDL cholesterol concentrations. The increase in LDL cholesterol was due to a significant increase in cholesterol content of the relatively buoyant LDL subfractions LDL1, LDL2 and LDL3, whereas the relative contribution of the dense LDL subfractions LDL4 and LDL5 to total LDL tended to decrease. So, both therapies resulted in a more buoyant LDL subfraction profile, reflected by a significant increase of the value of parameter K (+10.3% on Omacor vs. +26.5% on gemfibrozil therapy, gemfibrozil vs Omacor P>0.05). Cu(2+)-induced oxidation of LDL was measured by continuous monitoring of conjugated dienes. After 12 weeks of Omacor treatment LDL appeared more prone to oxidative modification in vitro than LDL after gemfibrozil treatment, as measured by the significantly decreased lag time, preceding the onset of the lipid peroxidation. In both groups the rate of oxidation did not change with therapy. The amount of dienes formed during oxidation increased significantly on Omacor treatment, but not on gemfibrozil treatment. Plasma thiobarbituric acid reactive substances were higher after Omacor and lower after gemfibrozil treatment, although not significantly. We conclude that both Omacor and gemfibrozil have favorable effects on lipid and lipoprotein concentrations and the LDL subfraction profile. However, Omacor increased the susceptibility of LDL to oxidation, whereas gemfibrozil did not affect the resistance of LDL to oxidative modification in vitro. The clinical relevance of these changes remains to be established in the light of other postulated favorable effects of n-3 fatty acids on the course of cardiovascular disease.

Biomarkers of oxidative stress: an analytical approach

Oxidative stress is implicated in many pathological processes and results from a disruption of the prooxidant/antioxidant balance. This review will focus on noninvasive biomarkers of radical-induced damage in biological fluids and particularly in blood. Special attention will be addressed to new analytical methods for the measurement of radical-mediated alterations in the integrity of lipids, proteins and DNA.

Low serum folate but normal homocysteine levels in patients with atherosclerotic vascular disease and matched healthy controls

Mild hyperhomocysteinemia has been considered a cardiovascular risk factor. However, recent prospective studies have not demonstrated that hyperhomocysteinemia or the underlying genetic defect on methylentetrahydrofolate reductase is associated with a higher risk of coronary or peripheral artery disease. We compared serum homocysteine, folate, and vitamin B(12) levels of patients with coronary and peripheral vascular disease with those of age- and sex-matched healthy individuals. Subjects taking multivitamins, with diabetes mellitus, or serum creatinine levels over 1.5 mg/dL were excluded from the study. Homocysteine was measured by fluorimetric high-performance liquid chromatography. Serum folate and vitamin B(12) levels were measured by an ion-capture method. We studied 32 patients with peripheral vascular disease (10 female), aged 69.6 +/- 11 y, 24 age- and sex-matched control subjects, 52 patients with coronary artery disease (7 female), aged 59.5 +/- 10.4 y, and 42 age- and sex-matched control subjects. Serum homocysteine levels were 11.7 +/- 7.4 and 9.3 +/- 4.5 micromol/L in vascular patients and in the control counterparts, respectively (not significant). The levels for coronary patients and the control counterparts were 9.0 +/- 3.9 and 8.6 +/- 3.6 micromol/L, respectively (not significant). Folate levels were 4.48 +/- 2.42 and 7.14 +/- 4.04 ng/mL in vascular patients and control subjects, respectively (P < 0.02); the levels in coronary patients and control counterparts were 5.15 +/- 1.9 and 6.59 +/- 2.49 ng/mL, respectively (P < 0.01). No differences in vitamin B(12) or tocopherol levels were observed between patients and control subjects. There were no differences in homocysteine levels, but lower serum folate levels were observed when comparing patients with atherosclerotic vascular disease and healthy control subjects.

Very low intakes of N-3 fatty acids incorporated into bovine milk reduce plasma triacylglycerol and increase HDL-cholesterol concentrations in healthy subjects

Eight normolipidaemic volunteers, habitual partial skim milk drinkers and non-eaters of fish during the study, were given 500 ml day(-1) of partial skim milk for 1 month; they were then switched to 500 ml day(-1) of a novel commercially available milk preparation, supplying 400 mg of N-3 fatty acids-of which 300 mg were EPA+DHA-and 15 mg vitamin E, for 6 weeks. No changes in plasma lipid parameters were observed after the first run-in month; at 3 and 6 weeks on the N-3-rich milk, marked increments of plasma EPA (44 and 31%, respectively) and DHA (13 and 31%, respectively) were observed. Triacylglycerol (TG) concentrations decreased by 19% and high-density lipoprotein (HDL) concentrations increased by 19% at 6 weeks; plasma vitamin E rose by 21% while the susceptibility of plasma to oxidation was unaffected. Correlations were found between plasma EPA or DHA and TG, cholesterol, and HDL. In conclusion, the intake of a milk preparation providing low amounts of EPA+DHA to healthy individuals led to marked increases of N-3 fatty acids and vitamin E in plasma and in associated favourable changes in HDL and TG.

In vitro differentiation of human monocytes to macrophages results in depletion of antioxidants and increase in n-3 fatty acids levels

The lipid composition and alpha-tocopherol content of human monocytes were investigated before and after their differentiation to macrophages. The total lipid and protein content per number of cells increased after the differentiation of monocytes by approximately four-fold; a two-fold increase in docosahexaenoic and docosapentaenoic acids and a two-fold decrease in linoleic acid were also noted. As opposed to an initial monocytic vitamin E content of 4.75 pmol/10(6) cells, macrophagic vitamin E levels were undetectable. Changes in vitamin E and fatty acids contents in macrophages, with respect to monocytes, appear to reflect the lipid composition of fetal calf serum, that is low in vitamin E and has a proportionally higher docosahexaenoic acid content than adult human serum.

Effect of n-3 polyunsaturated fatty acid supplementation on lipid peroxidation of rat organs

The present study was undertaken in order to reexamine the effect of n-3 polyunsaturated fatty acid (PUFA)-rich diet supplementation on lipid peroxidation and vitamin E status of rat organs. Male Wistar rats were fed a diet containing safflower or fish oil at 50 g/kg diet and an equal amount of vitamin E at 59 mg/kg diet (1.18 g/kg oil; and 1.5 g/kg PUFA in safflower oil diet, and 4.3 g/kg PUFA in fish oil diet) for 6 wk. Fatty acid composition of total lipids of brain, liver, heart, and lung of rats fed fish oil was rich in n-3 PUFA, whereas that of each organ of rats fed safflower oil was rich in n-6 PUFA. The vitamin E levels in liver, stomach, and testis of the fish oil diet group were slightly lower than those of the safflower oil diet group, but the levels in brain, heart, lung, kidney, and spleen were not different between the two diet groups. The levels of phospholipid hydroperoxides were determined by the high-performance liquid chromatography-chemiluminescence method and the levels of thiobarbituric acid-reactive substances (TBARS) were determined at pH 3.5 in the presence of butylated hydroxytoluene with or without EDTA. Levels of phospholipid hydroperoxides and TBARS in the brain, liver, heart, lung, kidney, spleen, stomach and testis of the fish oil diet group were similar to those of the safflower oil diet group. The results indicate that high fish oil intake does not induce increased levels of phospholipid hydroperoxides and TBARS in rat organs.

The kinetics of copper-induced LDL oxidation depend upon its lipid composition and antioxidant content

Copper promotes oxidation of human low-density lipoprotein (LDL) through molecular mechanisms that are still under investigation. We employed native human LDL, phospholipid-containing delipidated LDL ghosts, or trilinolein-reconstituted, phospholipid-containing LDL to investigate both LDL oxidation and the associated process of copper reduction. Both LDL ghosts and trilinolein-reconstituted LDL were devoid of antioxidants and were extremely susceptible to AAPH-induced oxidation but, paradoxically, were rather resistant to copper-mediated oxidation. The dynamic reduction of Cu(II) to Cu(I) was quantitatively decreased in LDL ghosts and in trilinolein-reconstituted LDL, also lacking the initial rapid reduction and the subsequent inhibition phases, due to the absence of endogenous antioxidants. Conversely, the rate of copper reduction was linear and likely due to lipid peroxides, either already present or formed during copper-induced oxidation. We suggest that copper undergoes redox transitions in LDL by utilizing reducing equivalents originating from endogenous antioxidants and/or from lipid peroxides in the LDL lipid core.

Effects of supplementation with folic acid and antioxidant vitamins on homocysteine levels and LDL oxidation in coronary patients

Hyperhomocysteinemia is an important cardiovascular risk factor. Serum homocysteine levels are specially dependent on folate nutritional status. In addition, the oxidative modification of low-density lipoproteins (LDLs) in the endothelial microenvironment is a damaging factor that can be modified with fat-soluble antioxidant vitamins. The present study was done to assess the effect of a supplementation of folic acid and antioxidant vitamins on homocysteine levels and in vitro LDL oxidation in patients with coronary artery disease. Twenty-three patients with angiographically proven coronary artery disease were given supplements for 15 d consisting of one capsule twice a day of a multivitamin preparation containing 0.65 mg folic acid, 150 mg alpha-tocopherol, 150 mg ascorbic acid, 12.5 mg beta-carotene, and 0.4 microgram vitamin B12. Serum lipids, vitamin and homocysteine levels, and in vitro LDL oxidation were measured before and after the supplementation period. During the supplementation period, serum folate levels increased from 5.0 +/- 1.5 to 10.8 +/- 3.8 ng/mL (P < 0.001), vitamin B12 increased from 317.4 +/- 130.4 to 334.5 +/- 123.8 pg/mL (P < 0.05), and alpha-tocopherol increased from 8.2 +/- 5.1 to 13.7 +/- 7.9 mg/L (P < 0.001). Serum homocysteine levels decreased from 8.7 +/- 4.3 to 6.3 +/- 2.2 mumol/L (P < 0.001). In vitro LDL oxidation decreased from 2.6 +/- 1.1 to 1.6 +/- 1.1 nmol malondialdehyde/mg protein (P < 0.001). In comparing patients with healthy controls, basal levels of folate were lower in the patients, whereas vitamin B12, alpha-tocopherol, and homocysteine levels were similar. No changes in serum lipid levels or body weight were observed. In conclusion, a short-term supplementation with folic acid and antioxidant vitamins can reduce serum homocysteine levels and in vitro LDL oxidation in patients with coronary artery disease.

Is glycation of low density lipoproteins in patients with Type 2 diabetes mellitus a LDL pre-oxidative condition?

AIMS

The study aimed to evaluate whether low density lipoprotein (LDL) in diabetic patients is more glycated and susceptible to oxidation than in non-diabetic subjects and investigated the hypothesis that LDL glycation is associated with an increased plasma concentration of LDL- (a circulating electronegatively charged LDL), proposed as an index of in vivo oxidation.

METHODS

LDL glycation was measured by a competitive enzyme immunoadsorbent assay, using a monoclonal antibody against glycated apoB in 24 Type 2 diabetic patients and 12 healthy controls. LDL- was separated by ion-exchange HPLC in LDL samples obtained after sequential preparative ultracentrifugation (density range 1.019-1.063). In vitro LDL susceptibility to oxidation was evaluated by following the kinetics of conjugated diene formation and by measuring the lag-phase time in the presence of copper (Cu2+) ions.

RESULTS

The percentages of glycated apoB (3.33+/-2.54% vs. 1.24+/-0.71%) and of LDL- (3.88+/-1.49% vs. 2.34+/-1.03%) in total LDL were significantly higher in diabetic patients (P<0.01 for both). LDL- was positively correlated with glycated apoB (r = 0.68, P<0.001). LDL isolated from Type 2 diabetic patients showed a significant decrease (P<0.001) in the resistance to oxidative stress, as indicated by the shorter lag-phase time (91+/-12.6 vs. 120+/-24.5 min). The lag-phase time was inversely correlated with glycated apoB (r = -0.65, P<0.001) and LDL- concentrations (r = -0.69, P<0.001).

CONCLUSIONS

In this population of Type 2 diabetic patients, LDL were more glycated, more susceptible to in vitro oxidation and had a higher percentage of electronegative LDL. The glycation of apoB is proposed to be associated with a significative increase of in vivo and in vitro LDL oxidation.

Arachidonic and docosahexaenoic acids differentially affect the expression of fatty acyl-CoA oxidase, protein kinase C and lipid peroxidation in HepG2 cells

Arachidonic (AA) and docosahexaenoic (DHA) acids (5-20 microM), when supplemented to human hepatoma HepG2 cells, which are depleted in these long-chain polyunsaturated fatty acids in conventional culture conditions, enhance the expression of acyl-CoA oxidase (ACOX), the first enzyme in the peroxisomal beta-oxidation cycle. DHA is effective at lower concentrations (at 5 microM) and to a greater extent (about 60% increment) than AA (about 40%) at 20 microM. Protein kinase C (PKC) appears to be involved in the activity of AA on ACOX, but not in that of DHA, since only the effect of AA is prevented by the PKC inhibitor Staurosporine, and since a remarkable elevation of the PKC activator diacylglycerol occurs only after AA supplementation. AA also induces elevation of lipoperoxides, favoured by the relative vitamin E deficiency occurring in cultured cells, and this effect, which is prevented by supplementation of the vitamin, may contribute to PKC activation.

Effect of uric acid and chemical analogues on oxidation of human low density lipoprotein in vitro

Oxidative modification of low density lipoprotein (LDL) is implicated in the early development of atherosclerosis. In the present study, attention has been focused toward the potential protective effects of uric acid and purine-based chemical analogues in copper-promoted oxidative changes to human LDL in vitro. Between 5-100 mumol/l uric acid protected LDL from oxidative degradation in a concentration dependent manner. However, 5 mumol/l were not capable of inhibiting the consumption of LDLs natural antioxidative components, alpha-tocopherol and beta-carotene, but led to a more than two-fold prolongation, up to 3 h, of the lag phase before onset of polyunsaturated acid (PUFA) oxidation. 100 mumol/l uric acid, which is still below the human serum level of 300 mumol/l, reduced consumption of alpha-tocopherol and beta-carotene by about 50% and largely suppressed PUFA oxidation for up to 4 h. A more lipophilic series of methyl analogues of uric acid exhibited less activity. Neither 1,3-dimethyl uric acid, nor the 1,3,7- or 1,7- or 3,7-methylated compounds, all at 100 mumol/l, exceeded the antioxidative potential of 10 mumol/l uric acid. At concentrations up to 100 mumol/l xanthine and its analogues lacked virtually any protective effects toward the LDL constituents. In conclusion, the present study indicates that uric acid at concentrations similar to its physiological levels, and also related analogues are able to suppress oxidative degradation of LDL components. In view of the various mechanisms underlying atherogenesis in vivo, the protective effect in terms of modulating redox reactions and oxidative events in the blood or at the arterial wall appears of potential importance.

Influence of fasting on circulating levels of alpha-tocopherol and beta-carotene. Effect of short-term supplementation

We investigated the influence of fasting on the levels of alpha-tocopherol in plasma, erythrocytes and platelets, and on plasma beta-carotene. Six apparently healthy adults were subjected to 17-h feed-fasting experiments at various days before, during and after supplementation with alpha-tocopherol (455 mg/day, 41 days) and beta-carotene (25 mg/day, 24 days). Adipose tissue alpha-tocopherol and beta-carotene were measured at regular intervals. Supplementation increased alpha-tocopherol and beta-carotene in all compartments, except for beta-carotene in adipose tissue. Discontinuation caused a rapid return to baseline, except for adipose tissue alpha-tocopherol and plasma beta-carotene. Fasting caused linear increases of free fatty acids, consistent (but small) increases of plasma alpha-tocopherol and inconsistent increases of plasma beta-carotene. There were no fasting-related changes in other compartments. We conclude that fasting is unable to increase alpha-tocopherol and beta-carotene in circulating lipoproteins and cells to a considerable extent, both at baseline levels and after short-term supplementation. Maintenance of high levels may necessitate regular high oral intakes.

Effect of n-3 fatty acid supplementation on lipid peroxidation and protein aggregation in rat erythrocyte membranes

Human erythrocytes in the circulation undergo dynamic oxidative damage involving membrane lipid peroxidation and protein aggregation during aging. The present study was undertaken to determine the effect of n-3 fatty acid supplementation on lipid peroxidation and protein aggregation in the circulation and also the in vitro susceptibility of rat erythrocyte membranes to oxidative damage. Wistar male rats were fed a diet containing n-6 fatty acid-rich safflower oil or n-3 fatty acid-rich fish oil with an equal amount of vitamin E for 6 wk. n-3 Fatty acid content in erythrocyte membranes of rats fed fish oil was significantly higher than that of rats fed safflower oil. The degree of membrane lipid peroxidation and protein aggregation of rats fed fish oil was not significantly higher than that of rats fed safflower oil when the amounts of phospholipid hydroperoxides, thiobarbituric acid-reactive substances, and detergent-insoluble protein aggregates were measured. When isolated erythrocytes were oxidized under aerobic conditions in the presence of Fe(III), the degree of membrane lipid peroxidation of erythrocytes from rats fed fish oil was increased to a greater extent than that of rats fed safflower oil, whereas the degree of membrane protein aggregation of both groups was increased in a similar extent. Hence, n-3 fatty acid supplementation did not affect lipid peroxidation and protein aggregation in membranes of circulating rat erythrocytes, and the supplementation increased the susceptibility of isolated erythrocytes to lipid peroxidation, but not to protein aggregation, under the aerobic conditions. If a sufficient amount of vitamin E is supplied, n-3 fatty acid supplementation may give no undesirable oxidative effects on rat erythrocytes in the circulation.

Oxidized low-density lipoproteins affect natural killer cell activity by impairing cytoskeleton function and altering the cytokine network

Several lines of evidence indicate that oxidative imbalance can play an important role in determining an impairment of natural killer (NK) cell activity in a variety of human diseases. Because a specific role for oxidized low-density lipoproteins (LDL) as pro-oxidizing agents has been envisaged, we tested the activity of oxidized LDL (ox-LDL) on NK cell-mediated cytotoxicity, cytokine release, and membrane molecule modulation. Native LDL served as control. Treatment with ox-LDL at noncytotoxic concentrations (0.2 mg/ml) during the NK/target cell (TC) interaction markedly reduced NK cytotoxic activity against U937 tumor cells. This inhibitory activity was also noticed when NK cells were pretreated with ox-LDL. Scanning electron microscopy examination of NK-target cell conjugates failed to reveal any morphological cell damage. In addition, the number of conjugates and the expression of some adhesion molecules (CD11a, CD11b, CD18, CD2, and CD62L) were not modified by ox-LDL. These observations argued against a possible interference of ox-LDL with the binding process leading to the formation of NK/TC conjugates. By contrast, immunocytochemical analyses of cytoskeleton components of NK cells exposed to ox-LDL showed a partial depolymerization and a derangement of the microtubular apparatus. These alterations were accompanied by an evident decrease in their intracellular reduced glutathione content. Owing to the important role played by the microtubular network during the killing process, it is possible to infer that a cytoskeleton alteration underlies the inhibitory activity of ox-LDL on NK cell function. In addition, exposure of mitogen-stimulated peripheral blood mononuclear cells to ox-LDL markedly reduced specific mRNA transcription and release of cytokines relevant for NK cell activity (such as tumor necrosis factor-alpha, interferon gamma, and interleukin 12). These data suggest that the impairment of NK cell activity by ox-LDL likely reflects the concomitant dysregulation of some essential mechanisms of NK cell function.

Brain and skeletal muscle bioenergetic failure in familial hypobetalipoproteinaemia

OBJECTIVE

To determine whether a multisystemic bioenergetic deficit is an underlying feature of familial hypobetalipoproteinaemia.

METHODS

Brain and skeletal muscle bioenergetics were studied by in vivo phosphorus MR spectroscopy (31P-MRS) in two neurologically affected members (mother and son) and in one asymptomatic member (daughter) of a kindred with familial hypobetalipoproteinaemia. Plasma concentrations of vitamin E and coenzyme Q10 (CoQ10) were also assessed.

RESULTS

Brain 31P-MRS disclosed in all patients a reduced phosphocreatine (PCr) concentration whereas the calculated ADP concentration was increased. Brain phosphorylation potential was reduced in the members by about 40%. Skeletal muscle was studied at rest in the three members and during aerobic exercise and recovery in the son and daughter. Only the mother showed an impaired mitochondrial function at rest. Both son and daughter showed an increased end exercise ADP concentration whereas the rates of postexercise recovery of PCr and ADP were slow in the daughter. The rate of inorganic phosphate recovery was reduced in both cases. Plasma concentration of vitamin E and CoQ10 was below the normal range in all members.

CONCLUSIONS

Structural changes in mitochondrial membranes and deficit of vitamin E together with reduced availability of CoQ10 can be responsible for the multisystemic bioenergetic deficit. Present findings suggest that CoQ10 supplementation may be important in familial hypobetalipoproteinaemia.

Plasma levels of lipid and cholesterol oxidation products and cytokines in diabetes mellitus and cigarette smoking: effects of vitamin E treatment

To evaluate the role of both oxidation and inflammation in atherosclerosis, we compared LDL oxidizability, in vivo lipid and cholesterol oxidation, and basal and lipopolysaccharide (LPS)-stimulated production of various cytokines in normolipidemic patients with diabetes mellitus (DM: n = 11), cigarettes smokers (n = 14). In addition, the effects of vitamin E (600 I.U./day for 4 weeks) on these parameters were evaluated. Initial LDL oxidation characteristics before and after vitamin E were identical in the 3 groups. Plasma thiobarbituric acid reactive substances were higher in DM and smokers versus controls (0.77 +/- 0.22, 0.74 +/- 0.14 versus 0.62 +/- 0.10 mumol malondialdehyde equivalents/l, respectively; P versus controls < 0.05) and normalized after vitamin E supplementation. Total plasma oxysterols were higher in smokers versus controls (354 +/- 104 versus 265 +/- 66 nmol/l, P < 0.05) and unaffected by vitamin E. The basal and LPS-stimulated levels of interleukin-1 beta and tumour necrosis factor alpha (TNF alpha) and the basal level of interleukin-1-receptor antagonist (IL-1RA) were identical for the 3 groups. LPS-stimulated IL-1RA was higher in DM versus controls (10.7 +/- 2.0 versus 8.1 +/- 1.7 pmol/l, P < 0.05). After vitamin E, TNF alpha dropped in controls and smokers, and IL-1RA in smokers only. Results suggest increased in vivo oxidative stress and inflammation in DM and smoking, which is partly overcome by vitamin E.

A rapid method for the determination of vitamin E forms in tissues and diet by high-performance liquid chromatography using a normal-phase diol column

This paper describes a simple method for the analysis of tocopherols in tissues by which frozen tissues-70 degrees C were pulverized at dry ice temperatures (-70 degrees C) and immediately extracted with hexane. There was no need to remove the coeluting lipids from tissues by saponification, since at that level of neutral lipids in the sample, there was no reduction in fluorescence response. For the analysis of oil, in which large amounts of neutral lipids were coextracted, a 20% reduction of fluorescence response was observed, but the response was equal for all tocopherol forms, and was appropriately corrected. Saponification was used only when tocopherol esters were present, and only after an initial hexane extraction to remove the free tocopherols in order to avoid their loss by saponification, particularly non alpha-tocopherol and tocotrienols. All the tocopherols and tocotrienols were separated on a normal-phase diol (epoxide) column that gave consistent and reproducible results, without the disadvantages of nonreproducibility with silica columns, or the lack of separation with reversed-phase columns. The tocopherols were quantitated by using a tocopherol form not present in the sample as an internal tocopherol standard, or using an external tocopherol standard if all forms were present, or when the sample was saponified. Piglet heart and liver samples showed the presence of mainly alpha-tocopherol, with minor amounts of beta- and gamma-tocopherol and alpha-tocotrienol, but no delta-tocopherol. Only small amounts of tocopherol esters were present in the liver but not in the heart.

Antioxidants inhibit the expression of intercellular cell adhesion molecule-1 and vascular cell adhesion molecule-1 induced by oxidized LDL on human umbilical vein endothelial cells

The oxidative modification of low density lipoprotein (LDL) and the endothelial expression of adhesion molecules are key events in the pathogenesis of atherosclerosis. In this study we evaluated the effect of oxidized LDL on the expression of intercellular cell adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin on human umbilical vein endothelial cells (HUVECs). The hypothesis that oxidized LDL functions as a prooxidant signal was also evaluated, by studying the effect of different radical-scavenging antioxidants on expression of adhesion molecules. LDL was oxidized by using Cu2+, HUVECs or phospholipase A2 (PLA2)/ soybean lipoxygenase (SLO), the degree of oxidation being measured as thiobarbituric acid-reactive substances (TBARS) and conjugated dienes (CD). Exposure of 200 micrograms/ml of native LDL to 1 microns Cu2+, HUVECs and to PLA2/ SLO resulted in four- to fivefold higher levels of TBARS and CD than in native LDL. Cu(2+)-(1 microM), HUVEC-, and PLA2/SLO-oxidized LDL caused a dose-dependent, significant increase of ICAM-1 and VCAM-1 (p < .01). The expression of E-selectin did not change. LDL oxidized with a 2.5 and 5 microM Cu2+ did not increase ICAM-1 and VCAM-1 significantly. Both the Cu(2+)- and HUVEC-oxidized LDL, subjected to dialysis and ultrafiltration, induced ICAM-1 and VCAM-1 expression. After incubation with the ultrafiltrate, the expression of ICAM-1 and VCAM-1 was not significantly different from that obtained with native LDL. LDL pretreated with different antioxidants (vitamin E and probucol) and subjected to oxidation by Cu2+ and HUVECs induced a significantly lower expression of ICAM-1 and VCAM-1 than nonloaded LDL (p < .01). The pretreatment of HUVECs with vitamin E and probucol significantly reduced the expression of VCAM-1 on HUVECs induced by oxidized LDL (p < .01); the effect on ICAM-1 was much less evident. In conclusion, oxidized LDL can induce the expression of different adhesion molecules on HUVECs; this induction can be prevented by pretreating either the LDL or the cells with radical-scavenging antioxidant.

Oxidized lipoprotein (a) induces cell adhesion molecule Mac-1 (CD 11b) and enhances adhesion of the monocytic cell line U937 to cultured endothelial cells

Because of structural similarities between low density lipoproteins (LDL) and lipoprotein (a) (Lp(a)), we have investigated the properties and the functional activities of oxidized Lp(a) and focused on whether oxidized Lp(a), like oxidized LDL, can induce monocyte differentiation and adhesion of monocytic cells to endothelial cells grown in culture. Oxidized Lp(a), prepared in vitro by cupric ion oxidation, gave absorption curves of conjugated dienes with a lag-phase of 61.7 +/- 6.6 min (mean +/- S.D.) as compared to 85.2 +/- 7.2 min (n = 6, P < 0.01) for oxidized LDL from the same donors and at equimolar concentrations. Degradation of oxidized 125I Lp(a) by the monocytic cell line U937 at 37 degrees C was 1.6 +/- 0.3 nmol/g of cell protein, significantly (P < 0.01) greater than the degradation of oxidized 125I-LDL, which was 1.15 +/- 0.2 nmol/g of cell protein. Equimolar concentrations of oxidized Lp(a) and LDL inhibited the growth of U937 by 82 +/- 8.2% and 64 +/- 7.1%, respectively, when compared with the effect (negligible) produced by native Lp(a) and LDL. In addition, equimolar concentrations of oxidized Lp(a) and LDL induced adhesion molecule, Mac-1 (CD 11b), expression in U937 by 64 +/- 7.1% and 58 +/- 6.1% (P > 0.05), respectively, of the effect produced by phorbol esters (PMA) (P < 0.01). U937 cells incubated with oxidized Lp(a) and LDL, showed an adherence to cultured endothelial cells at 42 +/- 5.2% and 34 +/- 4.8%, respectively (P < 0.05), of the adherence shown by the same cells activated by PMA (P < 0.01). Our results suggest that oxidized Lp(a) like oxidized LDL plays an important role in the development of atherogenesis by inducing adhesion of monocytes to the arterial intimal and by stimulating intimal monocytes to differentiate into macrophages.

Peroxynitrite inhibits glutamate transporter subtypes

The reuptake of glutamate in neurons and astrocytes terminates excitatory signals and prevents the persistence of excitotoxic levels of glutamate in the synaptic cleft. This process is inhibited by oxygen radicals and hydrogen peroxide (H2O2). Here we show that another biological oxidant, peroxynitrite (ONOO-), formed by combination of superoxide (O2-) and nitric oxide (NO), potently inhibits glutamate uptake by purified or recombinant high affinity glutamate transporters reconstituted in liposomes. ONOO- reduces selectively the Vmax of transport; its action is fast (reaching > or = 90% within 20 s), dose-dependent (50% inhibition at 50 microM), persistent upon ONOO- (or by product) removal, and insensitive to the presence of the lipid antioxidant vitamin E in the liposomal membranes. Therefore, it likely depends on direct interaction of ONOO- with the glutamate transporters. Three distinct recombinant glutamate transporters from the rat brain, GLT1, GLAST, and EAAC1, exhibit identical sensitivity to ONOO . H2O2 also inhibits reconstituted transport, and its action matches that of ONOO- on all respects; however, this is observed only with 5-10 mM H202 and after prolonged exposure (10 min) in highly oxygenated buffer. NO, released from NO donors (up to 10 mM), does not modify reconstituted glutamate uptake, although in parallel conditions it promotes cGMP formation in synaptosomal cytosolic fraction. Overall, our results suggest that the glutamate transporters contain conserved sites in their structures conferring vulnerability to ONOO- and other oxidants.

Study of causes underlying the low atherosclerotic response to dietary hypercholesterolemia in a selected strain of rabbits

We have recently characterized a strain of rabbits that shows a low atherosclerotic response (LAR) to dietary hypercholesterolemia in contrast to the usual high atherosclerotic response (HAR) of rabbits [1]. Presently, we have focused on three well established and important stages of atherogenesis, i.e., monocyte adhesion to endothelium, cell mediated peroxidative modification of lipoproteins and induction of a receptor that recognizes modified low density lipoprotein (LDL). The results obtained show that (1) beta-very low density lipoprotein (beta-VLDL) from LAR and HAR rabbits enhanced monocyte adhesion to endothelial cells to the same extent; (2) Cell mediated peroxidation of LDL and beta-VLDL, tested by loss of alpha-tocopherol and formation of thiobarbituric acid reacting substances (TBARS), was compared using macrophages, fibroblasts and smooth muscle cells (SMC) of LAR and HAR rabbits and no significant differences were found; (3) Induction of scavenger receptor by phorbol ester (phorbol 12-myristate 13-acetate (PMA)) and platelet-derived growth factor-BB (PDGF-BB) was determined in SMC or fibroblasts from LAR and HAR rabbits using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate-acetylated LDL (DiL-acLDL). We found a significantly higher uptake of DiI-acLDL in SMC and fibroblasts derived from HAR rabbits as compared with cells from LAR rabbits. Similar results were also obtained with [125I]-acLDL in fibroblasts from LAR and HAR rabbits with respect to cellular lipoprotein degradation after PMA pretreatment. Even though the attenuated atherosclerotic response to hypercholesterolemia of LAR rabbits may have multiple underlying causes, the most prominent so far is an apparent difference in inducibility of scavenger receptor in SMC and fibroblasts.

Relative resistance of the hamster to aortic atherosclerosis in spite of prolonged vitamin E deficiency and dietary hypercholesterolemia. Putative effect of increased HDL?

Male golden hamsters were rendered hypercholesterolemic by feeding diets enriched with cholesterol and fat. In the first series of experiments, 5% butter and 1% cholesterol were added to a chow diet and plasma cholesterol levels were maintained at 350-390 mg/dl over the entire experimental period. Groups of hamsters and their age controls consuming the chow diet, were killed after 7, 15 and 20 months when the aorta was examined for atherosclerosis by determination of cholesterol mass. In the controls, aortic total cholesterol (TC) increased with age by 28% and esterified cholesterol increased to 11% of TC. In the hypercholesterolemic animals aortic TC was only 28% higher than in the controls and cholesteryl ester was also 11.5% of TC. In the second series, one group of hamsters were fed a semi-purified diet deficient in vitamin E, containing 1% cholesterol and 10% lard; a second group received the same diet, but supplemented with vitamin E. Controls consumed local chow. After 7 months on the vitamin E deficient diet plasma alpha-tocopherol was 0.05 mg/l, in those supplemented with vitamin E it was 20 mg/l, while in the controls it was 3.3 mg/l. Plasma thiobarbituric acid reactive substances (TBARS) were higher in the vitamin E deficient group and there was a greater propensity of lipoproteins (d < 1.063 g/ml) to peroxidation in vitro than in the vitamin E supplemented group. Plasma cholesterol was 366 mg/dl in the vitamin E deficient, 336 mg/dl in the vitamin E supplemented group, and 64 mg/dl in controls. Aortic cholesterol was 79.1 in vitamin E supplemented and 84.4 micrograms/10 mg dry weight in vitamin E deficient hamsters. In both series of experiments, HDL amounted to 36-41% of plasma TC in the hypercholesterolemic animals and 59-62% in the controls.

IN CONCLUSION

the hamster appears to be quite resistant to atherosclerosis in face of sustained hypercholesterolemia, even in the presence of increased peroxidative stress caused by vitamin E deficiency. This relative resistance could be related to commensurate increase in plasma HDL which was observed in both series of experiments. Since vitamin E deficiency did not enhance aortic cholesteryl ester deposition, the protective effect of HDL seems to be related to its role in reverse cholesterol transport, rather than in prevention of peroxidation.

Plasmalogen phospholipids in plasma lipoproteins of normolipidemic donors and patients with hypercholesterolemia treated by LDL apheresis

Recent evidence indicates that plasmalogen phospholipids are particularly sensitive to oxidation and may possess antioxidative properties. Approximately 4.4%-5.5% of phosphatidylcholine (PC), and 53%-60% of phosphatidylethanolamine (PE) consisted of the plasmalogen phospholipids, plasmenylcholine and plasmenylethanolamine, respectively, in whole plasma, low density lipoprotein (LDL) and high density lipoprotein (HDL) of 11 normolipidemic donors. Of total plasmalogen phospholipids in plasma, slightly more was associated with LDL particles (about 42%) than with HDL (36%). Plasmalogen phospholipid levels were analyzed in 12 patients with familial hypercholesterolemia (FH) regularly treated by LDL apheresis, of whom 6 were supplemented with vitamin E (alpha tocopherol, 400 IU/day), the remaining 6 not receiving the antioxidant. Before apheresis (pre), total plasmalogen phospholipid levels in plasma and LDL (expressed as mumol/mmol cholesterol of compartment) decreased as follows: patients receiving vitamin E > normolipidemia > patients not receiving vitamin E. In both hypercholesterolemic groups, the contents of plasmalogen phospholipids in whole plasma and LDL were 3-5-fold higher than those of vitamin E. Directly after apheresis (post), plasmalogen phospholipid levels in plasma were raised by about 50% in the two hypercholesterolemic groups, mostly due to increases in plasmenylethanolamine levels. Two days after apheresis (48 h post), plasmalogen contents were still elevated in plasma and red blood cell membranes of patients receiving vitamin E, while they had already reached pre-apheresis values in those not supplemented with alpha tocopherol. Molecular species of plasma diacyl phospholipids containing polyunsaturated fatty acids were elevated at pre in patients receiving vitamin E as compared to patients without supplementation. At 48 h post, LDL apheresis induced an increase in these molecular species only in patients receiving vitamin E. In conclusion, the contents of plasmalogen phospholipids in plasma lipoproteins are at least three times higher than those of vitamin E. LDL apheresis raises the level of plasmalogen phospholipids in plasma, the increase persisting longer in patients supplemented with vitamin E. Supplementation with vitamin E appears to protect plasmalogen phospholipids in plasma lipoproteins against oxidative degradation.

Effects of exhaustive exercise and vitamin B6 deficiency on free radical oxidative process in male trained rats

There is growing evidence that oxygen free radical production and subsequent lipid peroxidation are normal sequelae to the rise in oxygen consumption concomitant with exercise. In addition, increased lipid peroxidation has also been shown in vitamin B6-deficient rat plasma, liver, and kidney. To investigate the potential for a role of vitamin B6 in exercise-induced oxidative stress, 36 male Sprague-Dawley rats received 0 (n = 12), 2 (n = 12), and 8 mg pyridoxine (PN)-HCl/kg diet (n = 12) and were trained by a 9-week swimming program. After 9-weeks of training, six rats (exhausted: E rats) of each vitamin group were exercised to exhaustion by swimming while the other six rats rested (nonexhausted: NE rats). Ascorbate, ascorbate free radical and antilipoperoxidant capability (AC) were evaluated in plasma. These parameters were higher in E rats than in NE rats. Free radical-mediated lipid peroxidation was measured in tissue and plasma by evaluation of thiobarbituric acid reactive substances (TBARS) content. This index of peroxidation was significantly increased in liver of E rats but not in plasma, heart, and gastrocnemius muscle. Concentration of TBARS in liver was the highest in vitamin B6-deficient rats (consuming 0 mg PN-HCl/kg diet) and the lowest in vitamin B6-sufficient rats (consuming 8 mg PN-HCl/kg diet). Vitamin E (alpha-tocopherol) levels in liver and heart were negatively related to vitamin B6 levels in the diet. Independently of vitamin B6, liver and muscle alpha-tocopherol levels were significantly higher in E animals than in NE animals. There is good evidence according to our results that exercise induced an oxidative stress, as indicated by a significant increase of ascorbyl radical levels in the plasma. The effects of vitamin B6 deficiency on the free radical metabolism are low in trained rats. On the contrary, exhaustive exercise induced modifications in the metabolism pathways of vitamin C and E objectivated by variations of levels of vitamin C in the plasma and vitamin E in liver.

Mechanisms involved in the in vitro modification of low density lipoprotein by human umbilical vein endothelial cells and copper ions

In this study we evaluated the time course and mechanism of low density lipoprotein (LDL) oxidation induced by human umbilical vein endothelial cells (HUVECs), cell-free medium (CFM) and Cu2+. After incubating LDL (200 micrograms/ml) with HUVECs, CFM and Cu2+ (concentration adjusted to obtain the same degree of LDL modification as with HUVECs), the extent of LDL lipid peroxidation and apoprotein B modification was monitored at different times from 0 to 24 h. This involved evaluating the time course of LDL conjugated diene, peroxide, malonyldialdehyde (MDA), fluorescence, relative electrophoretic mobility (REM), vitamin E and monounsaturated and polyunsaturated fatty acids. After incubation with HUVECs, the LDL REM was significantly higher than that obtained in CFM (p < 0.01). When balanced for the same degree of LDL modification as obtained with HUVECs, Cu2+ gave a REM similar to that obtained with HUVECs. At the different times of incubation there was no statistical difference between conjugated diene and peroxide values after incubation with HUVECs and with CFM. The values obtained with Cu2+ were significantly higher than those obtained with HUVECs and CFM (p < 0.01). MDA and LDL fluorescence were significantly higher after exposure to HUVECs than to CFM (p < 0.01), values being similar to those obtained with Cu2+. There was no statistical difference between the values of LDL oleic, linoleic, arachidonic and eicosapentaenoic acids after incubation with HUVECs and CFM. Eicosatetraynoic acid (ETYA), a lipoxygenase inhibitor, determined dose-dependent reduction of MDA formation induced by the incubation of LDL with HUVECs; it did not affect LDL conjugated diene. ETYA did not have any effect on the MDA derived from LDL after incubation with Cu2+ or CFM. The results of this study demonstrate that, unlike Cu2+, the contribution of HUVECs to LDL modification does not involve only lipid peroxidation of the lipoprotein; it also includes intracellular radical and non-radical processes.

Relations between copper, zinc and selenium intakes and malondialdehyde excretion after major burns

Copper, zinc and selenium are involved in free radical scavenging. As trace element status is altered after major burns, related free radical scavenging may be decreased: consequently lipid peroxidation, reflected by increased urinary malondialdehyde excretion (MDA), is considerably increased. This preliminary study aimed to investigate the relationship between trace elements and MDA excretion. Sixteen patients aged 34 +/- 9 years (mean +/- s.d.) burned over 37 +/- 11 per cent of body surface, were studied prospectively. Trace element balance studies from days 1 to 7 and serum and urine concentrations on days 10, 15, 20 and 25 were measured. The first 11 patients (groups 1--SBU < 80, and 2--SBU > or = 80) were given standard supplements and the five next patients increased supplements (group 3, SBU > or = 80). The MDA excretion from days 1 to 3 was correlated with burn severity (r = 0.59). The correlations between serum trace element levels after day 3 and MDA were negative: Cu, r = -0.065; Zn, r = -0.52; Se, r = -0.53. In Group 3, MDA excretion after day 3 decreased with increasing cumulative Zn (r = -0.46) and Se intakes (r = -0.57). It can be concluded that the MDA decrease after day 3 was not clearly attributable to the trace element supplements, but the negative trend observed between Zn and Se supplements and decreased MDA excretion requires further studies.

Low density lipoprotein oxidation is inhibited in vitro by olive oil constituents

Oxidation of low density lipoproteins maybe a factor in the development of atherosclerosis. The Mediterranean diet rich in vegetables, grains, legumes, fruits, and oils, mainly olive oil, has been suggested to reduce the incidence of coronary heart disease, because of its low saturated and high monounsaturated fatty acids content. It is also possible that the natural antioxidants in the oil help to prevent lipid oxidation, e.g. that of low density lipoproteins, thus retarding the formation of atherosclerotic plaques. First-pressed, extra-virgin olive oil contains appreciable amounts of polyphenolic compounds that prevent its autoxidation and are responsible for its high stability. We tested these compounds on low density lipoprotein oxidation and found an inhibitory effect, at low concentrations, on various indexes of lipid oxidation (vitamin E content, formation of thiobarbituric acid-reacting substances, lipid peroxides, levels of polyunsaturated fatty acids, protein modification, conjugated diene formation). Our data suggest that natural antioxidants could play a role in inhibiting the formation of cytotoxic products such as lipid peroxides thus retarding the onset of the atherosclerotic damage.

Formation of F2-isoprostanes in oxidized low density lipoprotein: inhibitory effect of hydroxytyrosol

Oxidatively-modified low-density lipoproteins (LDL) contribute to the onset of the atherosclerotic disease. A recently discovered marker of lipid peroxidation in a series of prostaglandin F2-like compounds, the prostaglandin isomers isoprostanes, that are generated from arachidonic acid through cyclooxygenase-independent pathways following free radical injury and are endowed with potent biological activities. The incidence of cardiovascular disease in the Mediterranean area is low, possibly because of the type of fat (mainly olive oil) and other components (e.g. fruits and vegetables) of the diet. Natural antioxidants abound in this kind of diet and may also contribute to the observed protection from coronary heart disease (CHD) by retarding the formation of the atherosclerotic plaque. Olive oil, the major dietary fat in the Mediterranean countries, is rich in phenols with antioxidant properties. We thus investigated the formation of isoprostanes during in vitro LDL oxidation and tested the effect of an olive-oil-extracted phenol (i.e. hydroxytyrosol). Our data show that production of isoprostanes and other markers of lipid peroxidation occurs during LDL oxidation and is inhibited by hydroxytyrosol.

Susceptibility of low density lipoprotein to oxidation in familial hypercholesterolaemia

There is increasing evidence that oxidative modification of low density lipoprotein (LDL) plays an important role in the pathogenesis of atherosclerosis. Subjects with familial hypercholesterolaemia (FH) have elevated concentrations of LDL and develop premature atherosclerosis. The aim of the study was to determine whether the susceptibility of LDL to in vitro oxidation is increased in FH subjects. LDL was isolated from 15 FH homozygotes (mean age +/- SD, 19 +/- 10 years; mean LDL-cholesterol 16.86 +/- 3.55 mmol/l), 15 FH heterozygotes (38 +/- 13 years; LDL-cholesterol 5.58 +/- 1.78 mmol/l) and 15 normocholesterolaemic subjects (31 +/- 8 years; LDL-cholesterol 3.07 +/- 0.77 mmol/l). Susceptibility of LDL to in vitro copper-mediated oxidation was assessed by measuring conjugated diene production at 234 nm, the lag phase being a measure of the resistance of LDL to oxidation. Unexpectedly, the mean duration of the lag phase was 2.2 fold longer in the FH homozygotes (123.8 +/- 45.0 min) and 1.75-fold longer in the FH heterozygotes (99.9 +/- 40.6 min) than in the controls (57.1 +/- 27.9 min; P < 0.0001). Serum and LDL vitamin E levels were higher in the FH patient, but not when expressed relative to LDL-cholesterol concentration. There was also no correlation between LDL vitamin E concentration and duration of the lag phase. LDL bulk rather than the susceptibility of LDL to oxidation is probably the more important factor for the initiation and progression of atherosclerosis in FH patients.